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Tree Measurements from a Small-footprint Multiple-return Airborne LIDAR

Under a cooperative agreement with the USDA, Forest Service, a multiple-return airborne scanning LIDAR is being investigated for use in identifying and measuring individual trees in coastal forest in the Pacific Northwest.

Multiple return systems are capable of detecting the elevation of several objects within the laser footprint of a single outgoing pulse. In Figure 1, this is illustrated using the red dots to simulate the many LIDAR returns.  The red line is one LIDAR pulse with 3 returns.  

The pulses from single return systems have already been successfully used to measure the height of the top of the tree canopy and underlying terrain in previous studies.  Investigation of the usefulness of the multiple return devices has yet to be completed.   Multiple return devices may provide additional information on the vertical structure of the forest.


Figure 1. Small-footprint Multiple-return Airborne

The objectives of the study were to estimate (Fig. 2):
  • tree height
  • crown area
  • number of trees per unit area
using multiple return airborne LIDAR.


Figure 2. Diagram of a simulated forest plot.

The data were acquired by EarthData http://www.earthdata.com/ over coastal forest in the Pacific Northwest near Bellingham WA, in October 1998 and July 1999.  In the first mission some 2,000ha (5,000 acres) were  covered, with an average distance between individual LIDAR measurements of 2m.  Subsets of this area were re-flown later at a higher density.



Terrain profiles, tree stems, tree crowns, and understory heights were measured in the field to provide ground reference data.



Results are not yet available from individual trees, but on a landscape scale, it seems that the LIDAR data have enabled the terrain and top surface of the canopy to be depicted at high resolution.  The terrain model produced from the LIDAR data appears to be very much more detailed than existing USGS products, which were derived photogrammetrically and cannot accurately measure ground elevations beneath vegetation. Work is currently proceeding on processing the terrain profiles and individual tree data.

Information extracted from multiple return LIDAR data (using procedures developed by EarthData)


Canopy Surface


Terrain Surface

Staff at the Engineering Research Center are developing a 3D immersive application for the virtual reality room at Mississippi State University, that provides researchers with tools for visualizations and analysis of LIDAR and other remotely sensed data.    ERC.MsState.Edu

Publications:

Visualization of Airborne Multiple-Return LIDAR Imagery from a Forested Landscape
Eggleston, Neil T.; Watson, Margaret; Evans, David L.; Moorhead, Robert J.; John W. McCombs II.  2000
Presented at the Second International Conference on Geospatial Information in Agriculture and Forestry,
Lake Buena Vista, Florida, 10-12 January 2000

A Virtual Reality Interface for Analyzing Remotely Sensed Forestry Data
Margaret Watson, Neil Eggleston, Derek Irby, Robert Moorhead, David Evans
Presented at the ACM SIGgraph conference, July 2000.

Contacts:

To learn more about visualizing information using virtual reality, contact:

Robert Moorhead
Professor, Electrical and Computer Engineering

Derek Irby
Research Assistant

To learn more about LIDAR applications in forestry, contact:

David Evans
Associate Professor, Forestry